Tuning Tips from Y to 1, 2, 3

3

What stands securely? Anything supported at 3 points. Surprisingly, most loudspeakers still have four contact points with the floor. That may be acceptable for equipment with rubber feet, but loudspeakers usually come with spikes and are therefore coupled rigidly to the floor. Inevitably, one of the four points will have a little more play, and that is a weak spot. Fortunately, it is easy to correct: place a small wooden block of the right height centrally at the front or rear and relieve the corresponding spikes.

Equipment in a rack also stands more securely on 3 points. Simple supports will do; ideally, one support - usually the one beneath the equipment's transformer - should be harder than the other two.

100 Hertz, or: External Noise

For me personally, this is a long story of suffering that finally ended well after five years. A few months after moving back into my old flat, I realised that something was wrong. I was having acoustic problems and had the feeling that I could hear something very faint in the background. By chance, a conversation with a neighbour in the rear building revealed that he had the same problem: noises in the flat, 24 hours a day, that simply did not belong there. We spent many nights searching for the cause, for a long time without success.
The breakthrough came with an ingenious Android app: Spectroid by Carl Reinke. As its name suggests, it is a spectrum analyser. It is astonishing what a smartphone microphone can measure.
In my flat, it revealed a very pronounced disturbance at exactly 100 Hz. Several sources are possible at this frequency: refrigerators, uncontrolled heating circulation pumps and transformers. As soon as it is connected to AC power, every transformer in Europe produces structure-borne sound at exactly 100 Hz due to the magnetostriction of its iron core. The strength of this sound does not depend on the power flowing through the transformer, but solely on its inductance.
Armed with this knowledge, I resumed the search and identified two medium-voltage transformers about 120 metres from my flat as the cause. The two transformers and my flat form a triangle with unequal sides and angles. One transformer was located in the basement of an Art Nouveau apartment building. The entire block where I live consists of old buildings joined together by masonry. The second transformer stood in a small building in a nearby park. In front of both transformers, the pavement could clearly be felt vibrating. Manhole covers within a radius of several hundred metres also vibrated, some more than others, because the two transformers formed an interference pattern. An inspection with the grid operator showed that the transformer in the residential building had inadequate vibration isolation, while the transformer in the park had none at all.
My neighbour and I were very fortunate that the responsible engineer was receptive. Tests were carried out: first the transformer in the park was switched off, which actually made matters worse because of the interference, and then both transformers were switched off or bypassed. The disturbance disappeared completely. There was no sound in my flat and no vibration from manhole covers within several hundred metres. The transformer in the residential building was permanently decommissioned, and the one in the park was replaced by a new transformer with double isolation against structure-borne sound.
One can speculate: was it coincidence that these two transformers were poorly isolated or not isolated at all? Was it coincidence that the effect was so strong in my flat? Medium-voltage transformers are installed every 300 to 500 metres in urban areas, so I fear I am not the only person affected. I must stress that this 100 Hz tone was not loud. It was subtle and gradually worked its way into one's awareness. A neighbour might not hear it at all because transformers this close together interfere with one another, and the energy may happen to cancel out at that particular location.
Since the problem was resolved, my system has sounded half a class better. Is that because the acoustic energy has disappeared from the room, or simply because I feel more comfortable in my flat?